ML22297A125
| ML22297A125 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 10/31/2022 |
| From: | Christian Jacobs Storage and Transportation Licensing Branch |
| To: | Division of Fuel Management |
| Shared Package | |
| ML22297A124 | List: |
| References | |
| EPID L-2022-LLA-0002 | |
| Download: ML22297A125 (1) | |
Text
Enclosure 1 Summary of request for additional information (RAI) discussion between Nuclear Regulatory Commission (NRC) staff and Holtec staff for: HI-2210161 Rev. 2, Topical Report on the Radiological Fuel Qualification Methodology for Dry Storage Systems RAI 1: OK RAI 2: OK RAI 3: (3b) Section 2.8.5 states that the water density for boiling water reactors (BWRs) is to be 0.3. Holtec needs to clarify if this is in fact water density or void fraction as there are no units and BWR moderators are usually described in terms of void fraction. The 0.3 value would be conservative as a water density (in g/cc) but non-conservative as a void fraction. In addition, Holtec should review the area of applicability for pressurized water reactor (PWR) moderator density as it seems very restrictive.
Response/Discussion:
Holtec believes 0.3 is water density but will verify. Holtec will also review PWR densities.
Holtec will clarify table 2.2 moderator densities are core average.
RAI 4: OK RAI 5: More details on the method used to generate the Co-60 source term from stainless steel replacement rods within reconstituted fuel is needed. Section 6.6 of ORNL/SPR-2021/2373 (https://info.ornl.gov/sites/publications/Files/Pub170905.pdf) shows that reconstituted fuel rods can have a significant effect on dose rates. Alternatively, since outer assemblies would be able to shield the Co-60 if its in an inner assembly, Holtec may restrict placement of reconstituted fuel to inner locations within the basket.
Response/Discussion:
NRC staff needs the details for these assemblies, but details seem to be scarce.
Alternatively, Holtec may want to consider putting in a restriction. Holtec is reluctant to include restrictions and would prefer to provide additional information with the specifics to answer the RAI.
RAI 6: OK RAI 7: OK RAI 8: OK RAI 9: (9a) Maximum mass needs to be added to the area of applicability in table 2.2 for non-fuel hardware (NFH) because this directly determines how much Co-60 is produced. Even though what is proposed is applicable to NFH in open literature, all NFH designs are not known nor are restrictions to future designs known which may have a larger impact if used for higher burnup fuel. Previous analyses that have shown that NFH is not a large impact on dose are typically from analyses that restrict these components to the inner assemblies, therefore, as an alternative, Holtec may restrict placement of NFH inserts to inner assembly locations as part of the use of this topical report. Note for underground or horizontal systems where outer assemblies may not obviously shield NFH in inner assemblies, additional studies or restrictions
would need to be placed on certain inserts that may have a larger contribution to dose to the top or bottom, such as (thimble plug devices) TPDs or (axial power shaping rod assemblies)
APSRs.
Response/Discussion:
This RAI is related to non-fuel hardware (NFH). This is an area that is not super well defined. Similar to the type of thinking for RAI 5 (i.e., restricting to the inner part of the basket), this issue would be resolved by putting in a restriction. Holtec questioned what NRCs concern is with the weight? Holtec does not see an impact to dose rates, because even though the weight has changed, the methodology has not changed. If Holtec wants to move to a more flexible mass insert, the Topical Report would need to be revised to address this. Right now, there is a fixed number for the mass weight in the Topical Report. Holtec will take a look to determine why the flexibility was removed. Holtec understands the NRC staffs question and will supplement their response.
Also, Holtec will update the Qualification Report (appendix E and F) as necessary.
RAI 10: (10b) Additional information is needed on the area of applicability in table 2.2 for neutron source assemblies (NSAs), see information related to RAI 9 above. Alternatively, similar to RAI 9 above, the gamma source term would be shielded by outside assemblies if NSA assemblies are limited to inner assemblies and restrictions on the placement to inner locations could be used in lieu of this additional information.
Response/Discussion:
This is a similar question to RAI 9, and Holtec will provide similar responses.
RAI 11
(11c) There is a typo on Step 2, For any NFH, develop the modeling in accordance with Sections 3.2, 3.5 or 3.5, as applicable. One of the 3.5 entries should be 3.4.
Response/Discussion:
Holtec will correct typo.
(11i) This item should be discussed with Holtec. The strategy for reducing the number of calculations proposed in section 2.6 (bottom of page 7) for regionalized loading is not clear and does not appear to take into account that some zones and source terms will have higher contribution to dose than others. A different strategy needs to be discussed that requires more representation of burnup, enrichment and cooling time (BECT) points in the outer zone(s) that contribute more to dose. In addition, since inner assemblies have a proportionally higher neutron contribution than gamma dose contribution, instead of randomly selecting from the inner zones, it would be more conservative to choose the BECT with the highest burnup for the inner zones. For underground or horizontal systems where, outer zones are not obviously the highest contributing zones, special considerations need to be proposed, otherwise all fuel qualification points need to be explicitly modeled.
Response/Discussion:
Holtec came up with a statistical approach to bound what would be put in. Holtec did not distinguish between outside and inside zones.
NRC staff would not characterize this is as a statistical approach, but more as a risk-informed approach (based on what contributes most to the dose). The intent is for zones (and also characteristics of the sources) contributing most to dose to be characterized appropriately. Holtec agrees with calling this a risk-informed approach and may modify the approach accordingly.
RAI 12: OK RAI 13: OK RSI 5: Appendix E and F which includes an example of the qualification report needs to be discussed with Holtec as it is currently presented as an alternative way of documenting the qualification report. In addition, several updates need to be made to these proposed tables consistent with the body of the topical report:
Burnup/enrichment/cooling time in appendix E and F is inconsistent with what topical allows in table 2.2.
Treatment of the Co-60 impurity needs to be added to the table Analysis of control rods if insertion is greater than 10%
Alternatives and justification if specific power is adjusted needs to be included Response/Discussion:
This question is regarding the Qualification Report. NRC staff stated that the regulatory review shifts from licensing to inspections if the Topical Report is approved. NRC staff is seeking efficiencies in addition to being risk informed. NRC staff is highly encouraging a consistent format to be used for this qualification report (not just be an alternative).
NRC staff is seeking to streamline this qualification report to make it more inspectable which would make the process more efficient. Holtec does not see an issue doing this, i.e., Holtec will create a template report that others could use.
NRC staff suggestion: sentence could be revised to something like "This appendix presents a recommended way of documenting..."
Holtec to ensure that appendix E and F are consistent with the main part of the report.